I'm on Act 1 of Nightmare difficulty with my Witch Doctor, and i have a weapon that has +150 intelligence and 20.6 DPS. yet i can make an axe at the smith that has 45+ weapon dps. is giving up that much intelligence worth the extra weapon damage?

Also. are the caster variant type classes (Wizard/Witch Doctor) in this game that reliant on weapon DPS as opposed to stacking intelligence? Because its taking me quite a while to kill things especially treasure goblins and elite monsters.

For the purpose of this question, we can ignore ability damage and bonuses from skills.

Understanding the Formula

Base Damage has two main components. Weapon Damage (this is the range you get, i.e. 4-6 for many starting weapons) and Primary Attribute bonus (this is 1% for every Primary Stat you ahve. In your case, Intelligence).

Because they are being multiplied, a small weapon range gets less benefit than a large one. 4-6 damage times 200% damage (from 100 intelligence) is only 8-12, whereas a weapon with 6-10 goes up to 12-20. The higher your weapon's average damage, the more valuable the bonus from stats is.

Applying our Findings

In your case, you've got a ton of Intelligence, which is great, and a really low damage weapon, which is less great. This means that really low damage is getting multiplied by a large value, which is still, unfortunately, in your case, a really low final value.

The take away here is that primary stat is not worth more than weapon damage. You need both to maximize your damage, which means you'd probably be best served by dropping your 20 dps weapon and picking up something nicer. As a comparison - My Wizard has a 33 DPS weapon, and she is only in Act III of Normal.

Add 100 to your current value of your primary stat. Divide it by your current weapon damage - remember to account for any bonuses from rings or other gear. That's roughly how much of your primary stat you'd need to make up for the loss of +1 Weapon Damage.

For example, using my numbers from here, I'd need 9 Dexterity to make up for the loss of 1 average weapon damage.

Incidentally, this is why Rings of Wounding are so absurdly good early in the game. When you have 20 in your primary stat and a 5 DPS weapon, those rings are worth somewhere on the order of 75 stat points. It takes a long time for the base DPS of your weapons and the stats available on gear to catch up to that.

Now partial derivative of that formula with respect to A, for example, is B * C * D * E = Damage/A.

So when one stats gets more and more that stats tend to worth less and less relative to other stats. The first 100 points of intelligence increase your DPS by twice. Once you have 1600 intelligence, every additional 100 point will add only a mere 6% DPS.

So to max out dps, you need to max out what you do not have. If you already have high intelligence, every increase damage will worth more. If you already have high damage, then intelligence and IAS worth more.

Exception is critical hit chance and critical damage. Those 2 are in synergy. Still for the same amount of money, it's easier to balance the 2 rather than one instead of the other.

When you want to max out DPS within monetary constrain, you'll see that moderate numbers from stats tend to add up DPS way more than extreme numbers of one particular stats. So spread out your damage maximizing stats.